Nor upon the future build one's hopes.

For the past has been left behind.
And the future's not yet reached.
Instead with insight let one see,
Each presently arisen state.
Let one know that and be sure of it,
Invincibly, unshakeably.
Today the effort must be made.
Tomorrow death may come.
Who knows?
No bargain with mortality can keep him and his hordes away. 
But for one who dwells thus ardently. 
Keeps at it, does not give up.
Practises by day, by night ---
It is those the peaceful sage has said
Who have had one excellent night. '

-- poem attributed to the Buddha